The presence of paraffin and asphaltene components (waxes) in hydrocarbon fluids can present a host of problems for the producer, transporter, and refiner of those fluids and of products obtained from those fluids. The presence of paraffin sand asphaltene components is similar to the formation of scale or rust. Their presence in the hydrocarbon reservoir, wellbore tubing, transfer lines, storage vessels, and pipelines can lead to serious problems. For a producing well, these components cause a steady fall off of production rates over time, eventually falling to unacceptable or unprofitable levels.
Upon the examination of hydrocarbon production reservoirs, it appears that most production reservoirs exhibit characteristics similar to a distillation process. After a production reservoir has been tapped, the light end hydrocarbon components are the first to leave. This departure begins: to increase the concentration of heavier liquid hydrocarbons within the reservoir. This causes a reduction in the reservoir pressure, thus reducing the drive efficiency of the well, and reduces the mobility of the heavier hydrocarbon fractions.
The lower reservoir pressure and the presence of less mobile, heavier hydrocarbon fractions reduce well production in a systematic, yet empirical graphic interpretation. It is known that moderation of production rates can reduce the deposition of wax and asphaltene, even though there may be a trade-off between the formation of naturally formed asphaltene and wax chokes. These natural chokes act as a speed control for the production rate of crude oil from a completed well. If these constraints are ignored, the consequences have a profound effect on the life expectancy of a producing site (i.e. reduced production). If the velocity when bringing oil to the surface is too slow, the probability of wax deposits is increased. Similarly, precipitation of the heavier fractions may occur due to environmental cooling as the fluid passes through low temperature zones. Another problem occurs when oil velocity is too high. The likelihood of asphaltene deposition is increased by the resulting increase in streaming potential.
Production rates from hydrocarbon wells decrease over time as the well becomes clogged with hydrocarbon deposits such as asphaltenes and paraffins. The industry has developed several technologies for addressing this problem, but each has limitations. These technologies are selected based on several criteria including the type of rock formation, subsurface conditions, the age of the field, and the cause of reduced production.
The most common technology involves injecting solvents, such as toluene, xylene or hot oiling the well in an attempt to dissolve the deposits. A common method involves injecting several hundred gallons of solvent downhole and following it with oil or water. Most material injected into the well will absorb back into the oil, and run into the tank battery. If the problem is bad enough then the material is swabbed into a tank. The oil is separated and the water and residual solvent is hauled to a disposal site. The principal problems are those encountered in the handling of these solvents, such as their toxicity to personnel handling them and the detrimental effects that could be caused to the surrounding soil and water if any amounts of these solvents are spilled.
Other methods inject surfactants downhole in an attempt to wash out the deposits. Newer methods inject biologically active microbes into the formation to consume the deposits. However, these methods have relatively high costs and/or present safety and environmental hazard issues that can be difficult to overcome.
Thus, there remains a need for an effective method of removing some or all of these paraffinic and/or asphaltene solids from a production well, without posing hazards to personnel or to the surrounding environment.